What do you think of the Derfflinger with 8-17in guns?

I tried the upgunned Derfflinger with 6-17in guns, and the design seemed undergunned. I added bulges and used 8-17in guns, 12-5.9in QF guns, and 4-88mm AA guns (with 4-50cm torpedo tubes). The dimensions are: 690ft x 95ft (100ft bulges) x 31ft. The Standard displacement is 31,014 tons. The speed is 26 knots, with a range of 5300nm at 14 knots. The lower belt is 11.8in with an upper belt of 9in. The deck is just 1.57in. This is the Springsharp report:

Derfflinger class upgunned, Germany Battlecruiser laid down 1914 (Engine 1911)

Displacement:
 29,292 t light; 31,014 t standard; 33,700 t normal; 35,849 t full load

Dimensions: Length overall / water x beam x draught
 696.85 ft / 690.29 ft x 95.14 ft (Bulges 100.07 ft) x 31.50 ft (normal load)
 212.40 m / 210.40 m x 29.00 m (Bulges 30.50 m)  x 9.60 m

Armament:
      8 - 16.93" / 430 mm guns (4x2 guns), 2,425.91lbs / 1,100.37kg shells, 1914 Model
   Breech loading guns in turrets (on barbettes)
   on centreline ends, evenly spread, 1 raised mount - superfiring
      12 - 5.91" / 150 mm guns in single mounts, 102.98lbs / 46.71kg shells, 1914 Model
   Quick firing guns in casemate mounts 
   on side, all amidships
      4 - 3.46" / 88.0 mm guns in single mounts, 20.79lbs / 9.43kg shells, 1914 Model
   Anti-aircraft guns in deck mounts with hoists
   on side, all amidships, all raised mounts - superfiring
 Weight of broadside 20,726 lbs / 9,401 kg
 Shells per gun, main battery: 90
 4 - 19.7" / 500 mm submerged torpedo tubes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 11.8" / 300 mm 410.11 ft / 125.00 m 9.84 ft / 3.00 m
 Ends: 3.94" / 100 mm 131.23 ft / 40.00 m 9.84 ft / 3.00 m
   148.95 ft / 45.40 m Unarmoured ends
 Upper: 9.06" / 230 mm 410.11 ft / 125.00 m 13.12 ft / 4.00 m
   Main Belt covers 91 % of normal length
   Main belt does not fully cover magazines and engineering spaces

   - Torpedo Bulkhead and Bulges:
  1.77" / 45 mm 410.11 ft / 125.00 m 29.53 ft / 9.00 m

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 10.6" / 270 mm 3.15" / 80 mm  10.6" / 270 mm
 2nd: 5.91" / 150 mm 1.97" / 50 mm  1.18" / 30 mm

   - Armour deck: 1.57" / 40 mm, Conning tower: 11.81" / 300 mm

Machinery:
 Coal fired boilers, steam turbines, 
 Direct drive, 4 shafts, 78,829 shp / 58,806 Kw = 26.00 kts
 Range 5,300nm at 14.00 kts
 Bunker at max displacement = 4,836 tons (100% coal)

Complement:
 1,243 - 1,616

Cost:
 £4.702 million / $18.806 million

Distribution of weights at normal displacement:
 Armament: 2,591 tons, 7.7 %
 Armour: 9,366 tons, 27.8 %
    - Belts: 4,414 tons, 13.1 %
    - Torpedo bulkhead: 794 tons, 2.4 %
    - Armament: 2,567 tons, 7.6 %
    - Armour Deck: 1,326 tons, 3.9 %
    - Conning Tower: 265 tons, 0.8 %
 Machinery: 3,519 tons, 10.4 %
 Hull, fittings & equipment: 13,816 tons, 41.0 %
 Fuel, ammunition & stores: 4,408 tons, 13.1 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   33,288 lbs / 15,099 Kg = 13.7 x 16.9 " / 430 mm shells or 4.7 torpedoes
 Stability (Unstable if below 1.00): 1.10
 Metacentric height 5.5 ft / 1.7 m
 Roll period: 17.9 seconds
 Steadiness - As gun platform (Average = 50 %): 60 %
   - Recoil effect (Restricted arc if above 1.00): 0.80
 Seaboat quality  (Average = 1.00): 1.21

Hull form characteristics:
 Hull has a flush deck
 Block coefficient: 0.542
 Length to Beam Ratio: 6.90 : 1
 'Natural speed' for length: 26.27 kts
 Power going to wave formation at top speed: 48 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 0.00 degrees
 Stern overhang: 6.56 ft / 2.00 m
 Freeboard (% = measuring location as a percentage of overall length):
    - Stem:  29.53 ft / 9.00 m
    - Forecastle (20 %): 19.69 ft / 6.00 m
    - Mid (50 %):  19.69 ft / 6.00 m
    - Quarterdeck (15 %): 19.69 ft / 6.00 m
    - Stern:  19.69 ft / 6.00 m
    - Average freeboard: 20.47 ft / 6.24 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 118.0 %
  - Above water (accommodation/working, high = better): 137.3 %
 Waterplane Area: 45,500 Square feet or 4,227 Square metres
 Displacement factor (Displacement / loading): 91 %
 Structure weight / hull surface area: 209 lbs/sq ft or 1,020 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.96
  - Longitudinal: 1.41
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent
 Good seaboat, rides out heavy weather easily